Depth-resolved fluorescence measurement in a layered turbid medium by polarized fluorescence spectroscopy

We show that, when a turbid medium with a layered fluorophore distribution is excited by linearly polarized light, measurement of angle-resolved polarized fluorescence can provide depth-resolved fluorescence measurements.     

Determination of the depth of a scattering target in a turbid medium with polarization discrimination of transmitted signals

We demonstrate the feasibility of a novel method of determining target depth in a turbid medium through Monte Carlo simulations and experiments. The method is based on the strong and weak dependencies of the copolarized component and the degree of polarization (DOP), respectively, of the transmitted intensity on the target depth. The two-way measurements of the copolarized intensity can be used for determination of target depth, whereas the transversely scanned DOP results are used for estimating the two-dimensional image in a turbid system. The combination of these two sets of data could provide useful results for estimating three-dimensional images.     

Simple time-domain optical method for estimating the depth and concentration of a fluorescent inclusion in a turbid medium

A simple time-domain optical method for estimating the depth and concentration of fluorescent inclusions in turbid media is described. We demonstrate direct depth estimation of a localized fluorescent object from the temporal position of the temporal point-spread function maximum. The depth estimation permits recovery of the fluorophore concentration, both of which are essential quantities for optical molecular imaging studies. Since the maximum is independent of the fluorophore concentration, excitation laser power, detector gain, and other system-dependent factors, this method ensures a robust and efficient approach.     

Estimating the depth and lifetime of a fluorescent inclusion in a turbid medium using a simple time-domain optical method

A simple time-domain optical method for estimating the depth (d) and lifetime (tau) of fluorescent inclusions in a turbid medium is described. We demonstrate the method for depth and lifetime estimation of a fluorescent inclusion directly by fitting a monoexponential decay (tau(eff)) of the temporal position of the temporal point-spread function and the measurement of its maximum temporal position (t(max)). Since both of these measurements are intensity independent, this method provides a robust and efficient approach. This method is validated with experimental data.     

Backscattering target detection in a turbid medium by use of circularly and linearly polarized light

The polarization properties of the backscattered light from a turbid medium containing large-diameter (10.143-microm) and small-diameter (0.202-microm) spherical polystyrene particles are studied. It is shown that the difference in the polarization properties of the emerging light that originates at the target and that is backscattered from the medium allows for improvement of image contrast by use of polarized light. Based on the images obtained by the CCD camera, the polarization memory effect with circularly polarized light is demonstrated to have an advantage over the linear polarization technique in imaging a highly reflective target inside a turbid medium containing large particles.     

A CTRW-based model of time-resolved fluorescence lifetime imaging in a turbid medium

We develop an analytic model of time-resolved fluorescent imaging of photons migrating through a semi-infinite turbid medium bounded by an infinite plane in the presence of a single stationary point fluorophore embedded in the medium. In contrast to earlier models of fluorescent imaging in which photon motion is assumed to be some form of continuous diffusion process, the present analysis is based on a continuous-time random walk (CTRW) on a simple cubic lattice, the objective being to estimate the position and lifetime of the fluorophore. This can provide information related to local variations in pH and temperature with potential medical significance. Aspects of the theory were tested using time-resolved measurements of the fluorescence from small inclusions inside tissue-like phantoms. The experimental results were found to be in good agreement with theoretical predictions provided that the fluorophore was not located too close to the planar boundary, a common problem in many diffusive systems.     

Optical characteristics of a turbid medium between two mirrors

Using the one-dimensional Boltzmann equation, we examine the optical scattering properties of a turbid medium that is located between two mirrors with controllable reflectivity. We examine how the mirrors can be used to enhance the total transmission of an intensity modulated laser beam through this system. The analytical results show that, for certain modulation frequencies, the total transmission can be increased if the laser source is placed between the mirrors. This finding could improve diffusive imaging for those highly scattering media that are so thick that the laser light would not penetrate sufficiently deep in the absence of any mirrors.     

A new scheme of the time-domain fluorescence tomography for a semi-infinite turbid medium

Optical Review - A new scheme for reconstruction of a fluorophore target embedded in a semi-infinite medium was proposed and evaluated. In this scheme, we neglected the presence of the fluorophore...     

Attenuation of a narrow light beam in a turbid medium

In model scattering media, in which the extinction coefficient and the probability of photon lifetime vary, the relation between the illumination near a parallel light beam and the optical depth is studied. It is shown that in media of low turbidity, Bouguer's Law holds at small penetration depths, because the scattered radiation is insignificant in comparison to the total energy balance. For beams of finite width, with constant , the illumination increases with increasing values. The importance of in relations describing the attenuation of a parallel light beam in turbid media is clarified.     

Multiple scattering of polarized light in a turbid medium

It is shown that multiple scattering of polarized light in a turbid medium can be represented as independent propagation of three basic modes: intensity and linearly and circularly polarized modes. Weak interaction between the basic modes can be described by perturbation theory and gives rise to “overtones” (additional polarization modes). Transport equations for the basic and additional modes are derived from a vector radiative transfer equation. Analytical solutions to these equations are found in the practically important cases of diffusive light propagation and small-angle multiple scattering. The results obtained are in good agreement with experimental and numerical results and provide an explanation for the experimentally observed difference in depolarization between linearly and circularly polarized waves.     

Heat transfer in a spherical turbid medium with conduction and radiation

The heat transfer through a spherical media with conduction and radiation is considered. The medium is considered to be turbid and anisotropically scattering with diffusely reflecting boundaries of constant temperatures. The radiative transfer problem is solved using the Galerkin method. An iterative method is used to solve the nonlinear relation between the radiative transfer equation and the conductive energy equation. Calculations are carried out and compared for a homogeneous, isotropically scattering medium with isothermal, transparent boundaries. The results show good agreement with previous work. Calculations are carried out for inhomogeneous media with isotropic, and forward and backward anisotropic scattering. The boundaries of the media are considered to be isothermal and may be transparent or diffusely reflecting boundaries. The calculations are used to study the effects of the single scattering albedo, the anisotropic scattering parameter, the conduction-radiation parameter and the heat source.     

位相型全息记录介质的浮雕深度和折射率变化的测量方法

本文提出了一种直接测量位相型全息记录介质的浮雕深度和折射率改变量的方法，它利用干涉显微镜及带ＣＣＤ摄像头的微机组成的简单系统，可获得很高的测量精度。本文分析了测量误差以及为使系统保持最高测量精度而应选取的最佳测量条件。     

Coherent backscattering of polarized light from a turbid medium

Approximate analytical expressions for the intensities of the polarized components of light reflected from a disordered medium with large discrete particles (larger than the wavelength) have been derived with the use of the method of decoupling of the vector transfer equation that is based on separate treatment of basic and additional polarization modes. The results obtained provide the relation between the peak shape in the angular distribution of the backscattered radiation with a given polarization and the optical characteristics of the medium and are in good agreement with experimental data and numerical calculations.     

Phase-shift interferometry measured transmission matrix of turbid medium: Three-step phase-shifting interference better than four-step one

Transmission matrix(TM) is an important tool for controlling light focusing, imaging, and communication through turbid media. It can be measured by 3-step(TM3) or 4-step(TM4) phase-shifting interference, but the similarities and differences of the transmission matrices obtained by the two methods are rarely reported. Therefore, we make a quantitative comparison of the peak light intensity, signal-to-noise ratio, and average background of 24 × 24 = 576 focal points between paired samples(TM3–TM4) through the Wilcoxon rank sum test, and discuss the singular value of the transmission matrix and the focal peak. The comparative results of peak light intensity and signal-to-noise ratio show that there is a significant difference between the 3-step phase shift and the 4-step phase shift transmission matrixes. The focusing effect of the former is significantly better than that of the latter; interest concentrates on the focal intensity and singular value. The reciprocal of the singular value is proportional to the squared intensity, which is in accordance with singular value theory. The results of comparison of peak light intensity and signal-to-noise ratio strongly suggest that 3-step phase shift should be selected and used in applying the phase shift method to the measurement of the transmission matrix; and the singular value is of great significance in quantifying the focusing, imaging, and communication quality of the transmission matrix.